1. Field of the Invention
The present invention relates to the preparation of diorganopolysiloxanes having alkoxy endgroups, designated PF (polymers containing functional groups) below, and to the use of such PF polymers as one of the essential constituents in single-component organopolysiloxane compositions which are stable in storage and in the absence of moisture, but which crosslink into elastomeric state under atmospheric humidity at ambient temperature, namely, cold-vulcanizable elastomer (CVE) compositions.
2. Description of the Prior Art
It is known to this art to prepare such PFs by reacting a dialkoxysilane, a trialkoxysilane or a tetraalkoxysilane with a diorganopolysiloxane oil comprising a hydroxyl group bonded to the silicon atom at each end of its polymer chain, but it is necessary to use a catalyst therefor. Indeed, numerous patents relate to the use of catalysts specifically for this reaction for the introduction of functional groups.
U.S. Pat. No. 3,542,901 describes an amine as the catalyst. This catalyst is effective, but the reaction is fairly slow (for example 15 to 30 min at 60.degree. C. for fairly reactive alkoxysilanes such as Si(OCH.sub.3).sub.4 or ViSi(OCH.sub.3).sub.3). With alkoxysilanes of low reactivity, it is necessary to employ very much longer reaction times, or to attain only incomplete reaction. It is also known that the presence of residual silanols is generally adverse to the stability of the system (see U.S. Pat. No. 4,489,191-A and also French published Patent Application Nos. 2,597,876 and 2,597,877). Moreover, it is difficult to remove the amine completely, which may have an adverse effect on the stability of the composition on storage thereof; it may also cause the appearance of yellowish discolorations, either during storage of the mastic or on the crosslinked product.
It is for this reason that numerous other catalytic systems have been proposed to the art. The following are exemplary:
(i) Potassium acetate: U.S. Pat. No. 3,504,051; PA1 (ii) Diverse inorganic oxides: FR 1,495,011; PA1 (iii) Organic titanium derivatives: U.S. Pat. No. 4,111,890; PA1 (iv) Titanate plus amine: U.S. Pat. No. 3,647,846; PA1 (v) Alkoxyaluminum chelate: GB-A-2,144,758; PA1 (vi) N,N'-Disubstituted hydroxylamine: FR-A-2,508,467; PA1 (vii) Carboxylic acid plus amine: FR 2,604,713; PA1 (viii) Carbamates: EP 0,210,402; PA1 (ix) Organic compounds containing an oxime group: FR 2,597,875. PA1 (a) 100 parts by weight of at least one straight-chain diorganopolysiloxane containing a hydroxyl group bonded to a silicon atom at each end of its polymer chain, with PA1 (b) 0.35 to 6 parts by weight of at least one polyalkoxysilane of the formula: EQU (R.sup.4).sub.c (R.sup.1).sub.a Si(OR.sup.2).sub.4-(a+c) ( 1) PA1 in which a is 0, 1 or 2; c is 0, 1 or 2; a+c is 0, 1 or 2; R.sup.1 is a substituted or unsubstituted, saturated or unsaturated, C.sub.1 to C.sub.13 aliphatic, cycloalkyl or aromatic monovalent hydrocarbon radical, which may include an epoxy, primary, secondary or tertiary amine or mercapto group; the radicals R.sup.2, which may be identical or different, are each an aliphatic organic radical having from 1 to 8 carbon atoms, in particular an alkyl radical, alkyl ether radical, alkyl ester radical, alkyl ketone radical or alkyl cyano radical, or an aralkyl radical having from 7 to 13 carbon atoms; and R.sup.4 is a substituted or unsubstituted, saturated or unsaturated, C.sub.1 to C.sub.13 aliphatic, cycloalkyl or aromatic monovalent hydrocarbon radical, with the proviso that R.sup.4 may be identical to R.sup.1, and PA1 (c) 0.5 to 15 parts by weight of at least one alcohol, preferably methanol.
Certain of these catalysts are slightly more active than the amines, but it is nevertheless necessary to heat the reaction medium to 60.degree. to 70.degree. C. in order to provide times of 5 to 10 minutes for introduction of the functional groups. Moreover, these catalysts, or the residues thereof, may have an adverse influence on the stability of the particular composition on storage, in particular in the presence of setting or curing catalysts, as well as on the properties of the crosslinked products because it is difficult or impossible to remove them completely after reaction.
Published Patent Application FR 88/15,312, filed Nov. 7, 1988 and assigned to the assignee hereof, also describes a process for the preparation of diorganopolysiloxanes having alkoxy endgroups, using lithium oxide as the catalyst for the introduction of functional groups.
Another process for preparing oils containing functional groups (PF) entails the utilization of mixed silanes having, in addition to the alkoxy groups, a water-soluble group such as an amido, amino, carbamate or oxime group, etc., if appropriate in the presence of a known catalyst for the introduction of functional groups and a polyalkoxysilane.
Processes of this type are described, in particular, in U.S. Pat. Nos. 3,697,568 and 3,896,079 and in EP-A-69,256.
These processes are effective, but require the use of costly mixed silanes. Moreover, the organic products resulting from the water-soluble groups after reaction may have an adverse effect on the CVE composition (see in this regard pages 4 and 5 of FR-A-2,543,562).